1. Field of the Invention
The present invention relates to a process for removing residual acids including acetic acid and acrylic or methacrylic acids from ethylene copolymers such as ethylene vinyl acetate or ethylene acrylic acid or ethylene methacrylic acid or ionomers thereof. The process is also directed to the removal of residual monomeric alkyl acrylates which may be present in the ethylene copolymers.
2. Description of Related Art
Residual acids or monomeric alkyl acrylates formed during the production process of ethylene copolymers have presented a continual technical problem, especially if the packaging material or wire and cable material or other fabricated material is utilized to package or contain acid or monomeric alkyl acrylate sensitive contents or material.
The use of a certain kind of zeolite to remove offensive odors or flavors is known. For example, WO 95/20624 published on Aug. 3, 1995 describes the use of an adsorption agent which is added to films made from ethylene/acid copolymers to absorb odors. The siliceous material described therein is selected from those molecular sieves having a framework of tetrahedral oxide units, in which at least 90% of the tetrahedral oxide units are SiO tetrahedral, have a pore diameter greater than 5.5 Angstroms (preferably at least 6.0 Angstroms) and have a sorption capacity for water of less than 10% by weight at 25xc2x0 C. and 4.6 Torr (preferably less than 6% by weight). The preferred sieves are also described as having a framework SiO2/Al2O3 molar ratio of greater than 35, more preferably 200-500. This invention is also described in U.S. application Ser. No. 08/676,237. These molecular sieves are known to be hydrophobic in that they sorb less than 10 wt. % water at 25xc2x0 C. and 4.6 Torr pressure.
The present invention, on the other hand, is directed to the use of a completely different molecular sieve for a particular purpose-the scavenging or removal or unwanted acid from ethylene copolymeric material which is utilized to contain or package acid or monomeric acrylate sensitive material. The recited molecular sieves utilized in this invention are hydrophilic in nature (e.g., absorb greater than 10% water at 25xc2x0 C. and 4.6 Torr pressure) and are thus different than that described and used in the above patent publication.
The present invention broadly relates to a process for removing unwanted acid or monomeric acrylate from an ethylene/acid copolymer comprising,
i) preparing a thermoplastic composition comprising an ethylene/acid copolymer or ionomer thereof or an ethylene/acid/acrylate terpolymer or ionomer thereof or an ethylene/vinyl acetate copolymer wherein the composition contains residual acid, and
ii) adding to the composition an acid scavenging agent selected from a hydrophilic molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 100 and having a nominal pore diameter of 8-10 Angstroms. The preferred ratio is less than 35 and most preferred ratio is less than 3.0.
The invention further relates to a process as described above wherein the molecular sieve preferentially absorbs acetic acid over water.
The present invention also relates to a method for packaging or containing an acid sensitive material comprising,
i) preparing a film or material comprising a thermoplastic composition comprising an ethylene/acid copolymer or ionomer thereof or an ethylene/acid/acrylate terpolymer or ionomer thereof or an ethylene/vinyl acetate copolymer and an acid scavenging agent selected from a hydrophilic molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 100 (or less than 5 35 or less than 3.0) and having a nominal pore diameter of 8-10 Angstroms and
ii) packaging said film or material with the acid sensitive material. The material to be packaged, such as surgical sutures, can be packaged in such a way that the packaged material does not actually contact the packaging surface but, the packaged material may still be exposed to fumes of acid which would come from the packaging material if the zeolite was not present.
The present invention also relates to a thermoplastic composition comprising an ethylene/acid copolymer or ionomer thereof or an ethylene/acid/acrylate terpolymer or ionomer thereof or an ethylene/vinyl acetate copolymer and an acid scavenging agent selected from a hydrophilic molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 100 (or less than 35 or less than 3.0) and having a nominal pore diameter of 8-10 Angstroms. The invention also relates to a peelable seal composition comprising (a) a zeolite concentrate which comprises an ethylene acid copolymer or ionomer thereof and a hydrophilic molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 100 (or less than 35 or less than 3.0) and having a nominal pore diameter of 8-10 Angstroms and (b) a blend of (i) an ethylene acid copolymer or ionomer thereof and (ii) a polyolefin resin selected from a homopolymer or copolymer of polybutylene or blends of such polymers with polypropylene; or a homopolymer or copolymer of polypropylene and further to this peelable composition coated onto an aluminum surface or a primed aluminum surface wherein the primer is selected from a mixture of ethylene acid copolymer or ionomer thereof and the above zeolite. The invention further relates to a composition as recited above wherein the molecular sieve preferentially absorbs acetic acid over water upon exposure of said composition to an aqueous/acetic acid environment.
The present invention additionally relates to a multilayer packaging structure comprising,
(a) an innermost layer comprising a thermoplastic ethylene copolymeric composition comprising an ethylene copolymer and a zeolite selected from a molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 100 (or less than 35 or less than 3.0) and having a nominal pore diameter of 8-10 Angstroms; and 
(b) at least one additional polymeric, metallic or non-metallic layer. This additional polymeric layer may be selected from the same generic material as the inner layer (a) (e.g. both layers do not have to be but may be identical) or may be selected from a layer containing an ethylene copolymeric packaging material which is, for example, an ethylene/acid copolymer or ionomer containing film which does not have the molecular sieve contained therein or from a polyester or other common packaging material. Such materials are sold under the trade names NUCREL(copyright) (ethylene acid copolymer) or SURLYN(copyright) (ethylene acid ionomer). The metallic layer may be selected from a common packaging material such as aluminum. The multilayer structure can include additional layers as necessary to form the desired package provided that at least one of the layers is (a). The peelable seal composition described above can be extrusion coated onto a single layer or multilayer structure to form the multilayer structure containing said composition as a layer. The peelable seal composition can also be coextrusion coated onto an aluminum surface of a multilayer aluminum substrate wherein a tie layer having a tie composition is the coextrusion component and actually contacts the surface of the aluminum. The tie layer can comprise an ethylene acid copolymer/zeolite concentrate wherein the zeolite is type 13X.
As summarized above, the present invention relates to a thermoplastic ethylene copolymeric composition comprising an ethylene copolymer and a zeolite selected from a molecular sieve which comprises a sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and having a silica/alumina ratio of less than 3.0 and having a nominal pore diameter of 8-10 Angstroms. This composition is particularly useful in the manufacture of articles which are ultimately destined to contain or package acid sensitive materials such as surgical sutures and the like.
The ethylene copolymers and terpolymers utilized herein are selected from a wide variety of commercially available polymers which incorporate ethylene as a basis monomeric unit and incorporate at least one additional comonomer selected from vinyl acetate, acrylic acid, methacrylic acid. Additional monomers may also form part of the polymeric structure and these may be selected from esters such as alkyl acrylates and the like. A common feature of the non-ethylene monomers is the presence of a carboxylic acid moiety or precursor to such moiety. Additional acid containing monomers may be selected from diacids such as maleic or fumaric acid or their anhydrides. The acid containing monomer may comprise up to fifty percent of the polymer. Methods of preparing such copolymers are disclosed in, for example, U.S. Pat. Nos. 3,264,272; 3,404,134; 3,355,319 and 4,321,337 which are hereby incorporated by reference. Examples of these polymers can be obtained commercially under the trade names ELVAX(copyright) (ethylene vinyl acetate) which is used in a variety of end use applications including as a major component in wires and cables; NUCREL(copyright) (ethylene/methacrylic acid copolymer optionally containing an additional softening monomer such as methyl acrylate) and SURLYN(copyright) which is a metal ionomer of the above ethylene methacrylic acid copolymer or terpolymer. Other alkyl acrylates may be selected from n-butyl acrylate or isobutylacrylate. lonomers are neutralized either in whole or in part to form metal salts of the acid containing copolymers. These cations are generally selected from metals such as sodium or potassium or zinc or ther known metal salts or mixtures of these.
Preferred thermoplastic ethylene copolymers are selected from copolymers of ethylene and 2-50%, more preferably 5-25T, by weight of acrylic or methacrylic acid neutralized up to about 90%, more preferably 5-60% with an alkali metal ion or a divalent or trivalent metal ion, the melt index of the copolymer being about 0.1-30 or preferably about 0.5-20 dg/min. according to ASTM standard D1238. In addition to selection of these copolymers or terpolymers, the present invention may also include adhesive compositions containing an acid containing polymeric material such as an acid modified (grafted) polymeric material such as EPDM, EPR or other known material which is capable of being acid modified and incorporated into an adhesive composition. As suggested above, since the copolymers contain an acid containing monomer as a component, residual acid containing monomers may remain in the batch after polymerization and extrusion or blow molding of film or fabricated parts produced from such copolymeric material. The residual acid may also be a natural degradation product of the acid containing ethylene copolymer. Likewise, is adhesives containing an acid modified or anhydride modified ethylene copolymer such as those sold under the trademark BYNEL(copyright) may contain trace amounts of unreacted modifier or may contain decomposition products which include acid containing groups. In any case, the final film product or wire and cable or other fabricated part or material or adhesive contains an amount of acid which, absent incorporation of the molecular sieve described below, could affect or harm acid sensitive material which comes in contact with the film, fabricated part etc.
The molecular sieve suitable for use in the invention is selected from a hydrophilic sodium aluminosilicate containing less than 5 wt. % of magnesium oxide and has a silica/alumina ratio of less than 100 and a nominal pore diameter of eight to ten Angstroms. Preferred sieves have a silica/alumina ratio of less than 35 and the most preferred sieves have a ratio of less than 3.0. It is believed that functionality for acid scavenaging can be accomplished with the silica/alumina ratios described above. The preferred sieve is generically known as xe2x80x9cType 13Xxe2x80x9d and is sold under the name MOLSIV(copyright) 9356. This molecular sieve is typically utilized as a surface modifier for polyester film. Other molecular sieves which may also be suitable include products made by UOP sold under the trademark MOLSIV(copyright) 9356 and ABSCENTS(copyright) 1000 and 2000 which have silica/alumina ratios of less than 100. The molecular sieve has an average particle size of less than 5 microns. The molecular sieve is utilized and referred to as an xe2x80x9cacid scavengerxe2x80x9d which also includes adsorption of residual monomeric alkyl acrylates from the ethylene copolymers or terpolymers which form the other primary component of the composition.
The term xe2x80x9chydrophilicxe2x80x9d is defined as those molecular sieves which absorb greater than 10% water at 25xc2x0 C. and 4.6 Torr pressure.
The thermoplastic composition containing both the ethylene copolymers and the molecular sieve is generally prepared by mixing or blending (compounding) the components before extrusion or formation of a film, adhesive or fabricated part. The amount of molecular sieve added to the ethylene copolymer resin depends upon the particular acid content of the ethylene copolymer as well as the acid sensitivity of the product which is to be packaged or exposed to the packaging material made from the thermoplastic composition. Typically the sieve will comprise at least 0.5% by weight of the composition, more typically 0.5-2.0% by weight of the final film or end product and can also be made as a concentrate which is diluted with pure resin as needed. The ratios in this latter case will vary considerably. The amount of sieve in the final composition may also be as low as 0.1 wt. % if some acid removal is required.
In addition to the above-mentioned composition components, the composition or materials made therefrom may further include other additional components including polymeric components as well as ingredients or additives conventionally employed in the art for various purposes in polymer compositions, such as dyes, pigments, fillers, antioxidants, fire-retarding agents etc. When such optional excipients are included, they are present in a weight percentage or loading level that is typical for that particular excipient.
Films, adhesives, wire and cable elements or other fabricated parts containing the above thermoplastic compositions are prepared according to conventional means such as extrusion, blow molding, cast film processing or injection molding. Peelable seal layers as packaging material may be formed from the thermoplastic composition and used to package or wrap acid sensitive materials such as surgical sutures. Film layers made from the compositions of the invention may be utilized as the internal layer of a multilayer structure which is utilized to wrap or package acid sensitive material. Absorption of the acid or acid material internally (from within the polymer in the form of a composition as claimed herein) prior to its use as a packaging material is superior to placement of an acid-scavenging coupon within the package along with the acid sensitive material. In the latter case, acidic vapors from an untreated polymer can migrate into the headspace of the package and contact the acid sensitive product prior to absorption by the coupon. A similar situation occurs when it is desired to absorb unpolymerized monomer from the polymer prior to its use as a packaging material.
In the case of ethylene/vinyl acetate wire and cable insulation, the process of vulcanizing a semiconductive composition made from this polymer usually is carried out at a temperature at which the polymer is not very stable. The instability is evidenced by liberation of acetic acid that can cause corrision of the metallic conductor and thus, premature failure. Incorporation of the acid-scavenging agent prevents the acetic acid from contacting the conductor and therefore contributes to maintaining maximum use life.